<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>05流程控制</title>
</head>
<body>
<script>
  //顺序结构
  console.log(1);
  console.log(2);
  console.log(3);

  //分支结构
  let username = '';
  if(!username){//若用户名为空字符串，转为布尔是false，!false为true，走分支1
    alert('用户名不能为空');
  }else {
    alert('欢迎'+username+'回归');
  }

  //循环分支
  let names = ['张三','李四','王五'];
  for (let i =0;i< names.length;i++){
    console.log(names[i]);
  }
  console.log(i);
</script>
</body>
</html>